With a higher energy density and a longer cycle life, a lithium ion battery has become the most important power source of a portable electronic product and an electric automobile.
Generally, graphite materials are used for the negative pole material of a commercial lithium ion battery, because graphite materials have a high cycle stability during the process of lithium intercalation and extraction.
However, graphite materials encounter a lot of problems in practice. For example, the theoretical capacity of graphite materials is only 372 mAhg-1, and therefore hardly satisfies the requirement of high energy density of the lithium ion battery.
In addition, with a high theoretical reversible specific capacity, a metal oxide is also widely used to manufacture a large-capacity and high-energy density lithium ion battery. However, during the cycle process of metal oxide materials, the capacity sharply decreases in the initial irreversible reaction and the subsequent cycle process, resulting in a low cycle stability of the lithium ion battery.
In recent years, nanocrystallization of materials, especially use of one-dimensional nano structure, greatly improves the mechanical strength of the materials during the process of lithium intercalation and extraction, thereby enabling the materials to sustain a greater tension, and maximally maintaining structural integrity of the materials during the process of charge and discharge of the lithium ion battery. In this way, features of the negative pole of the lithium ion battery are effectively improved. For example, the one-dimensional nano structure of the metal oxide is used for the negative pole of the lithium ion battery, which may also effectively improve the cycle stability of the materials. However, due to limitations of the metal oxide materials, the reversible specific capacity and cycle stability of the metal oxide materials still fail to satisfy the application requirements of the commercial lithium ion battery.
Therefore, a novel negative pole is needed for the lithium ion battery, for improving the reversible specific capacity and cycle stability of the lithium ion battery.
In the prior art, metal oxide and carbon materials are compounded. This, in one aspect, improves the reversible specific capacity of the carbon material; and in another aspect, improves the cycle stability of the metal oxide material. Referring to Chinese Patent Application No. CN201010291060.5, graphene and stannic oxide are compounded and used for the negative pole of a lithium ion battery, achieving an initial reversible specific capacity of over 1000 mAhg-1 for the material. After cycling 20 times, the specific discharge capacity still remains at 600 mAhg-1. This greatly improves a performance of the negative pole of the lithium ion battery on which only a carbon material and a metal oxide material are applied.
Although this technical solution improves the reversible specific capacity and cycle stability of the lithium ion battery to some extent, the reversible specific capacity and cycle stability are still not satisfactory.